Allowable Substrate Bias for the Etching of n-GaN hi Photo-Enhanced Electrochemical Etching

Etching characteristics for n-GaN on bias voltage were examined in various chemical solutions including the solutions not considered as etchants. n-GaN was not etched in HNO₃ and CH₃COOH solutions during photo-enhanced electrochemical (PEC) etching under UV illumination of 90 mW/cm². It was successfully etched in 1% CH₃COOH solution by applying a bias larger than 0.6 V and the etch rate was increased to 23 nm/min at 1.5 V. Also, etching of n-GaN began to appear at 0.4 V in 0.05% HNO₃ solution. On the contrary, n-GaN was etched at a rate of 12 nm/ min in 0.04M KOH solution and 6 nm/min in 0.01M H₃PO₄ solution even though the bias was not applied and -0.4 and -0.3 V were needed to stop the etching of n-GaN, respectively. The increase of etch rate on the reverse bias was shown for all the examined solutions and the critical bias for n-GaN etching was not varied on the UV illumination intensity.